The present invention relates to techniques for manufacturing assemblies of molded parts, and more particularly to techniques for manufacturing a throttle valve disc within a throttle body.
Air flow valves include a flow control blade or disc which fit into a bore in a throttle body which defines an air flow passage. The disc is pivoted on a shaft to open and close the flow passage, and must fit accurately to be able to rotate between a closed position allowing a low flow of air and open positions. With machined or stamped metal parts, a sufficiently accurate fit has been obtained by a technique of centering the disc at assembly.
However, where the valve body and the valve disc are both molded of a non-metallic material, a difficult manufacturing problem is encountered due to the close tolerances required for a proper fit. One difficulty is assuring that the outer periphery of the disc contacts the inner bore while having a substantially constant thickness. Typically, a fixed upper and lower forming support form the disc within the bore of the throttle body. However, the disc material or thickness may be inconsistent prior to the final forming operation. If one portion of the disc is thicker than another portion, the rigid support may squeeze the thick portion first and provide an inconsistent disc perimeter thickness. This may slow the time to process the disk to a required minimum airflow in the throttle body.
Accordingly, it is desirable to provide a manufacturing process for molding an accurately fitted valve disc of an air flow valve which provides a controllable outer periphery thickness and can be carried out without a complex mold configuration.
The forming assembly according to the present invention includes a first support insertable into a bore of an air flow assembly such as a throttle body system having a valve disc within a bore. For descriptive purposes, the first support is inserted into the bore from below the valve disc, and a second support inserted from above the disc. Each support includes an integral heater for heating and forming of the disc and a pair of relatively narrow semi-circular or semi-elliptical style forming segment.
The second support floats relative to the disc upon a fluid receiving member such as an inflatable bellows. A support structure extends from the second support to retain the fluid receiving member. The support structure is preferably manufactured of a thermally insulated material such that heat from the heaters is not conducted to the fluid within the fluid receiving member. An arbor preferably having an outwardly extending flange engages an inwardly extending flange of the support structure such that the airflow assembly is locatable within and removable from the forming assembly. The fluid such as hydraulic oil is maintained in a supply and is pumped through the arbor and into and out of the fluid receiving member.
A method according to the present invention includes moving the first support into contact with the disc while substantially simultaneously moving the second support into contact with an opposite side of the disc. Importantly, the fluid receiving member allows the second support to xe2x80x9cfloatxe2x80x9d when engaging the disc. As the fluid receiving member allows the second support to xe2x80x9cfloatxe2x80x9d when contacting the disc, any inconstancies of the disc are compensated by the xe2x80x9cfloatingxe2x80x9d second support. In other words, if one portion of the disc is thicker than another portion, the second support pivots or cants to compensate for the disc surface. Fluid is pumped through the arbor and into the fluid receiving member such that the disc is squeezed between the first and second support. As the disc is squeezed between the supports heat conducted from the heaters causes the material of the disc to be extruded radially outwardly into contact with the bore. Deformation of the disc is monitored and controlled by a controller which monitor the volume of fluid which is pumped into the fluid receiving member.
Once the thermoforming operation is complete and the desired thickness at the perimeter of the disc is obtained, the fluid pressure within the fluid receiving member is relieved. The supports may then be withdrawn from within the system.
The present invention therefore provides a manufacturing process for molding an accurately fitted valve disc of an air flow valve which provides a controllable outer periphery thickness and can be carried out without a complex mold configuration.